Oh E, Wurster D E, Majuru S, Wang J C
University of Iowa, College of Pharmacy, Iowa City, Iowa 52242, USA.
J Pharm Sci. 1998 Sep;87(9):1124-9. doi: 10.1021/js970473c.
Vapor adsorption isotherms of two nonpolar model compounds, heptane and 1,4-dioxane, were determined for a very small particle size zinc oxide (ZnO) powder (median particle size approximately 23 nm) in the lower relative vapor pressure (P/Po) region. The ZnO samples for all adsorption measurements were dried at 400 degrees C for 4 h. A new method, which employed an FTIR spectrometer with a long path gas cell (IR path length of 3.0 m), was developed for the organic vapor adsorption measurements. The amount adsorbed was determined by mass balance. This method allows accurate quantification of organic vapors and is sensitive to very low P/Po values. The heptane and 1, 4-dioxane vapor adsorption isotherms appeared to exhibit the expected Type II behavior. The surface areas obtained for ZnO from BET analyses of the heptane and 1,4-dioxane vapor adsorption isotherms (36.9 and 30.3 m2/g) compared reasonably well to the surface area obtained from BET analysis of the nitrogen vapor adsorption isotherm (32.6 m2/g). The amount of vapor adsorbed by ZnO at P/Po equal to 0.1, in terms of number of moles, was observed to decrease in the order: water10 >> 1,4-dioxane > heptane. It was inferred that, while heptane was only adsorbed via a dipole-induced dipole interaction, 1,4-dioxane was physically adsorbed via an interaction dominated by the oxygen lone-pair orbital. Presumably, this interaction was more comparable to a weak dipole-dipole interaction. These results are consistent with the expected strengths of interaction.
在较低的相对蒸汽压（P/Po）区域，测定了两种非极性模型化合物庚烷和1,4 - 二氧六环在粒径非常小的氧化锌（ZnO）粉末（中位粒径约23 nm）上的蒸汽吸附等温线。用于所有吸附测量的ZnO样品在400℃下干燥4小时。开发了一种新方法，该方法使用带有长程气室（红外光程长度为3.0 m）的傅里叶变换红外光谱仪进行有机蒸汽吸附测量。吸附量通过质量平衡确定。该方法能够准确量化有机蒸汽，并且对非常低的P/Po值敏感。庚烷和1,4 - 二氧六环的蒸汽吸附等温线似乎呈现出预期的II型行为。通过对庚烷和1,4 - 二氧六环蒸汽吸附等温线的BET分析得到的ZnO表面积（36.9和30.3 m²/g）与通过氮气蒸汽吸附等温线的BET分析得到的表面积（32.6 m²/g）相当吻合。观察到在P/Po等于0.1时，ZnO吸附的蒸汽量（以摩尔数计）按以下顺序减少：水 >> 1,4 - 二氧六环 > 庚烷。据推断，虽然庚烷仅通过偶极 - 诱导偶极相互作用被吸附，但1,4 - 二氧六环是通过以氧孤对轨道为主导的相互作用被物理吸附。据推测，这种相互作用更类似于弱偶极 - 偶极相互作用。这些结果与预期的相互作用强度一致。
